The present invention relates to a light emitting device applicable to an optical-assisted magnetic recording head, the optical-assisted magnetic recording head, and an optical-assisted magnetic recording device.
As a typical example for the conventional optical-assisted magnetic recording system, for example, Japanese Unexamined Patent Publication No. 4-176034/1992 (Tokukaihei 4-176034, published on Jun. 23, 1992) discloses a high density magnetic recording system. In this high density magnetic recording system, adopted is a magnetic recording medium having a film laminated structure on a transparent substrate, and a laser beam is projected on the magnetic recording medium from the side of the substrate to be focused at a portion right below a magnetic recording head section by an optical lens, thereby locally heating the magnetic recording medium. As a result, the coercive force of the heated portion is reduced, and further by applying thereto a magnetic field using the magnetic recording head, a high density recording operation can be realized.
The foregoing techniques on the optical-assisted magnetic recording system can utilize conventional techniques on a magnetic recording head or an optical system used in magneto optical recording, and therefore permit developments of various new systems in combination with the existing technology with ease. Further, since a magnetic recording operation can be performed in an overlapped area between the magnetic head and the laser beam spot, a still finer bit recording can be performed, thereby realizing a high density magnetic recording.
In the foregoing conventional techniques, however, in order to realize high density magnetic recording, a high precision servo system is required for the positioning of a magnetic recording head and a laser focusing position. Besides, with the above conventional system, it is difficult to perform a both-sided magnetic recording.
In response, Japanese Patent No. 2881983 (issued on Apr. 12, 1999, (Japanese Unexamined Patent Publication No. 4-67451/1992 (Tokukaihei 4-67451), published on Mar. 3, 1992)) discloses a magneto-optical recording technique which solves the above problem although the optical-assisted magnetic recording technique is not adopted. This Japanese patent discloses the laser focusing technique from the side of a coil for use in magnetic recording using a composite magnetic recording head wherein an optical system for focusing a laser beam and the coil for use in magnetic recording are combined. In this technique, the both sides of the recording medium can be utilized. Therefore, the foregoing laser focusing technique is applicable to not only the conventional single-sided magneto-optical recording but also both-sided magneto-optical recording. Moreover, with the described technique, the servo system for use in positioning the magnet coil and the laser light spot can be omitted, thereby simplifying the overall structure of the system.
However, in the magneto-optical recording adopting the above composite magnetic recording head, an optical lens system is adopted for focusing, and therefore the head becomes complicated in structure, larger in size and heavier, yet high precision is required for the relative positioning of the coil and the optical system.
Moreover, when forming a super resolution image of a laser utilizing the apotization effect using a conventional lens, a phase shift occurs due to aberration of an optical system, particularly an aberration of the lens, resulting in a broader intensity distribution of the laser beam. The above super resolution image enables recording and reproduction in a smaller area than a beam spot utilizing the intensity distribution of the laser beam at a beam spot. In this case, it is therefore not possible to utilize the effects of high density recording and reproduction by the super resolution image effectively. On the other hand, in order to eliminate the aberration of the lens, an optical system of a complicated structure or a high precision optical lens is required.
In the described conventional composite magnetic recording head, the problems in terms of productivity and the cost remain unsolved.
By the way, in order to realize an optical-assisted high density magnetic recording, it is required to reduce the laser spot diameter and to have a sharp magnetic field distribution at the center of the laser spot.
In the conventional composite magnetic recording head adopting the optical lens, however, it is not possible to reduce the laser spot diameter to not more than 100 nm by the effect of optical diffraction. Moreover, in the above conventional magneto-optical recording system, the magnet coil and the magnetic recording medium are positioned at a large interval, and therefore, a sharp magnetic field distribution cannot be obtained at the center of the laser spot.
It is an object of the present invention to provide a light emitting device for focusing a laser beam without adopting an optical lens system, and also to provide a composite magnetic recording head and a magnetic recording device, which realize a smaller laser spot diameter and a sharp magnetic field distribution, whereby an optical-assisted high density magnetic recording can be realized, and which also realize a simplified head structure, and improvements in productivity and costs.
In order to obtain the above object, the present invention realizes an optical-assisted magnetic recording by utilizing the microfabrication technique. Specifically, for example, by adopting a composite magnetic recording head wherein a magnet coil and a main magnetic pole are formed directly at a laser aperture serving as a laser emitting surface of a surface-emitting semiconductor laser (light source), a laser beam is focused at portion right below a shielding member by the apodization effect, thereby realizing the optical-assisted magnetic recording.
In the present invention, the laser aperture is defined as a laser beam emitting area (an area through which the laser beam is emitted), and in the case of limiting the emitting area by a shielding member such as mask, etc., as other area than the shielded area by the shielding member, through which the laser beam can be projected.
In general, when the radius of the laser aperture is around a half wavelength of the laser beam, and the laser aperture and the irradiation surface (in the present invention, the surface of the magnetic recording medium) are positioned at an interval of not more than 100 nm, the light beams emitted from the periphery and the center of the laser aperture are attenuated one another on the irradiation surface at portion right below the aperture for the following reason. That is, respective paths of the laser beams emitted from the center and the periphery of the laser aperture are displaced from one another by around the radius of the laser aperture, i.e., the half wavelength, and the respective light beams are therefore countervailed. In response, for example, a shielding member may be formed at the center of the aperture so as to shield the light beam projected from the center of the laser aperture. In this way, it becomes possible to focus the light projected from the periphery of the laser aperture on the irradiation surface at portion right below the shielding member. The described phenomenon is called xe2x80x9capodization effectxe2x80x9d.
By utilizing the foregoing apodization effect, a laser beam of a desired intensity can be obtained by adjusting the area of the aperture. Further, by providing the shielding member at the center of the aperture, it becomes possible to focus the laser beam at portion right below the shielding member. In the foregoing method of emitting a light beam, a passive optical system can be omitted, thereby simplifying the structure of the light emitting device.
In order to achieve the above object, the light emitting device of the present invention is characterized by including:
a light source for emitting a laser beam having a wavelength xcex, wherein a laser aperture serving as a laser emitting surface has a radius R within the range of:
xcex/2+axcexxe2x89xa6Rxe2x89xa61.3xcex+axcex (a is 0 or a positive integer (axe2x89xa70)); and
a shielding member for shielding only a laser beam, which passes through a predetermined area at a center of the laser aperture, of all laser beams which pass through the laser aperture.
According to the foregoing structure, the apodization effect of the laser beam appears. The laser beam can be focused without using the lens.
In order to achieve the above object, the magnetic recording head of the present invention which includes a light source for emitting a laser beam and a magnet coil for use in magnetic recording, is characterized in that the magnet coil is integrally provided with the light source at around a center of the laser aperture serving as the laser emitting surface of the light source.
According to the foregoing structure, by adopting the light source and the magnet coil which are formed in one integral part, a magnetic recording can be performed from the side of emitting a laser beam. With the foregoing positioning of the light source and the magnet coil, a perpendicular magnetic field can be applied onto the surface of the aperture at the center of the laser aperture, and the foregoing structure is therefore effective in performing a perpendicular magnetic recording. Further, by reducing the radius of the magnet coil formed at the center of the laser aperture to a size of several xcexcm, it is possible to apply a strong magnetic field at around the center of the laser aperture.
In order to achieve the above object, the magnetic recording device of the present invention is characterized by including:
light emitting means, which includes a) a light source for emitting a laser beam having a wavelength xcex, wherein a laser aperture serving as a laser emitting surface has a radius R within the range of: xcex/2+axcexxe2x89xa6Rxe2x89xa61.3xcex+axcex (a is 0 or a positive integer (axe2x89xa70)), and b) a shielding member for shielding only a laser beam, which passes through a predetermined area at a center of the laser aperture, of all laser beams which pass through the laser aperture; and
a magnet coil for applying a magnetic field onto a magnetic recording medium,
wherein the light emitting means forms a light spot by focusing a laser beam onto the magnetic recording medium using the shielding member; and
the magnet coil applies the magnetic field for use in magnetic recording in an area including a light spot forming region of the magnetic recording medium.
According to the foregoing structure, the light emitting means is arranged so as to include the light source for emitting a laser beam having a wavelength xcex, wherein the laser aperture has a radius R within the range of xcex/2+axcexxe2x89xa6Rxe2x89xa61.3xcex+axcex (a is 0 or a positive integer (axe2x89xa70)), and the shielding member for shielding only a laser beam, which passes through a predetermined area at a center of the laser aperture, of all laser beams which pass through the laser aperture. As a result, a laser spot can be formed by the apodization effect onto the magnetic recording medium at portion right below the shielding member.
With the foregoing structure, it is possible to perform a high density magnetic recording in an overlapped area between a thermal distribution of a magnetic recording medium generated by the laser spot focused at portion right below the shielding member and a magnetic flux distribution as applied by the magnet coil.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.